Sucrose is the first form of carbohydrate to leave photosynthesizing cells in most higher plants and is the main form of transported carbon in most annual field crops plants such as corn, soybeans and wheat. As such its movement and concentration across various plant membranes is critical to plant growth and development. In addition sucrose is the main form of carbon that moves into developing seeds of soybeans, corn and wheat. This movement and concentration is accomplished by the action of sucrose carrier proteins that act to move sucrose against a concentration gradient by coupling sucrose movement to the opposite vectoral movement of a proton. Specific sucrose carrier sequences from these crop plants should find use in controlling the timing and extent of phenomena such as grain fill duration that are important factors in crop yield and quality. Accordingly, the availability of nucleic acid sequences encoding all or a portion of these enzymes would facilitate studies to better understand carbohydrate metabolism and function in plants, provide genetic tools for the manipulation of these biosynthetic pathways, and provide a means to control carbohydrate transport and distribution in plant cells.